Field of the Invention
The present invention relates to a joined unit of glass base members, an airtight envelope, and a method for producing a glass structural unit. The present invention is applicable especially preferably to an envelope of, for example, a display which includes a device therein and a method for producing the same, wherein it is feared for the device that the performance may be deteriorated by the invasion of any gas such as oxygen, water or the like.
Description of the Related Art
A technique has been hitherto known, in which opposing glass base members are joined to one another in an airtight manner to form an internal space having the airtightness. This technique is applied to a method for producing an airtight envelope of a flat panel including, for example, the vacuum heat insulating glass, the organic LED display (OLED), the field emission display (FED), and the plasma display panel (PDP). When the airtight envelope as described above is produced, then a joining material is arranged at circumferential edge portions of glass base members, and the glass base members are joined to one another, for example, by means of the heating, provided that a spacing distance defining member, a local adhesive and the like are arranged between the opposing glass base members, if necessary. A method has been suggested as a method for mutually joining the glass base members, wherein an assembly, which is obtained by temporarily assembling the glass base members, is entirely heated (baked) as a whole by means of a heating furnace. Another method has been also suggested, wherein only the circumferential edge portions of the assembly are selectively heated by a local heating means. The local heating is more advantageous than the whole heating in view of the heating and cooling time, the reduction of the energy required for the heating, and the prevention of any thermal deterioration of the functional device contained in the case.
United States Patent Application Publication No. 2008/0171485 discloses an example in which the airtight joining using the laser beam is applied to a method for producing an envelope of OLED by making use of the advantage of the local heating. In this production method, a frit, which is arranged between two glass base members, is firstly heated and melted by a first laser beam to join the glass base members to one another. Subsequently, a second laser beam is radiated onto the joined area to anneal the joined area. Owing to the anneal effect brought about by the second laser beam, the occurrence of any glass breakage, which would be otherwise caused in any inappropriate direction during a cutting step to be performed thereafter, is avoided.
Japanese Patent Application Laid-open No. 2003-286048 discloses a technique in which the breaking strength or fracture strength of a glass base member is enhanced by a laser beam having an extremely short pulse width. In this technique, a heterogeneous phase is formed in the glass base member by radiating the laser beam having the extremely short pulse width onto the glass base member. The heterogeneous phase is a compressive stress layer which is formed in the vicinity of the surface of the glass base member. The strength of the glass base member is enhanced by the formation of the compressive stress layer formed in the vicinity of the surface of the glass base member.
U.S. Pat. No. 5,820,435 discloses a method for producing an envelope of FED. In this production method, a frame member and a joining material (frit) are firstly arranged at circumferential edge portions of a first glass base member and a second glass base member which are arranged oppositely. Subsequently, a laser beam is intermittently radiated along with a direction in which the joining material extends so that the discrete partial joining is obtained. Subsequently, the laser beam is continuously radiated onto the entire circumference of the joining material including the partially joined area so that the continuous airtight joining is obtained.
Japanese Patent Application Laid-open No. 2000-313630 discloses a method for producing fused glass. In this production method, a joining material (frit) is firstly arranged at circumferential edge portions of a first glass base member and a second glass base member which are arranged oppositely. Subsequently, a light source, in which local heating light sources for the pre-heating, the joining, and the gradual cooling are arranged closely to one another in this order, is used to continuously radiate a laser beam onto the entire circumference of the joining material while performing the scanning so that the continuous airtight joining is obtained. The laser radiation is performed in the three stages for the purpose of the pre-heating, the joining, and the gradual cooling. Therefore, the temperature distribution of the radiation objective is gentle, and it is easy to avoid the crack. In the pre-heating stage, the joining material is heated to a temperature which is less than the glass fusion temperature. Therefore, any fusion of glass is not caused.
Japanese Patent Application Laid-open No. 2006-315902 discloses a method for joining two substrates of a display apparatus. In this joining method, a sealing material is firstly arranged at circumferential edge portions of a first glass substrate and a second glass substrate which are arranged oppositely. Subsequently, a first laser beam, which has a wide radiation range and which is capable of simultaneously heating the sealing material and the substrates disposed therearound, is radiated simultaneously with a second laser beam which has a narrow radiation range and which has a high absorptance or absorption factor with respect to the sealing material. The first laser beam has the wider radiation range. Therefore, the sealing material is firstly heated by the first laser beam to such an extent that the sealing material is not melted. After that, the sealing material is heated and melted by the second laser beam.
United States Patent Application Publication No. 2007/0128966 discloses a method for joining two substrates of a display apparatus. In this joining method, a second substrate is arranged so that the second substrate is brought in contact with a joining material (frit) arranged on a first substrate. A laser beam is radiated onto the joining material while performing the scanning at a velocity of 5 mm/s to 300 mm/s. Thus, the two substrates are joined to one another.